Many vessels in animals transport fluids from one body location to another. Frequently, fluid flows in a substantially unidirectional manner along the length of the vessel. For example, veins in the body transport blood to the heart and arteries carry blood away from the heart.
Recently, various implantable medical devices and minimally invasive methods for implantation of these devices have been developed to deliver these medical devices within the lumen of a body vessel. These devices are advantageously inserted intravascularly, for example from an implantation catheter. For example, implantable medical devices can function as a replacement venous valve, or restore native venous valve function by bringing incompetent valve leaflets into closer proximity. Such devices can comprise an expandable frame configured for implantation in the lumen of a body vessel, such as a vein. Venous valve devices can further comprise features that provide a valve function, such as opposable leaflets.
Dynamic fluctuations in the shape of the lumen of a vein pose challenges to the design of implantable prosthetic devices that conform to the interior shape of the lumen of a vein. Unlike arterial vessels, the flow velocity and diameter of veins does not remain essentially constant at a given systemic vascular resistance. Instead, the shape of vein lumens can fluctuate dynamically in response to the respiration, body position, central venous pressure, arterial inflow and calf muscle pump action of a mammalian subject. The veins also provide the principal volume capacitance organ. For example, an increase of almost 100% in the diameter of the common femoral vein has been observed in human patients simply by rotation of the patient by about 40 degrees, corresponding to a four-fold increase in blood flow volume. Moneta et al., “Duplex untrasound assessment of venous diameters, peak velocities and flow patterns,” J. Vasc. Surg. 1988; 8; 286-291. Therefore, the shape of a lumen of a vein, which is substantially elliptical in cross-section, can undergo dramatic dynamic change as a result of varying blood flow velocities and volumes therethrough, presenting challenges for designing implantable intraluminal prosthetic devices that more closely conform to the changing shape of the vein lumen.
Implantable devices for treating venous valve insufficiency are often not designed to be responsive to dynamic changes in the shape of a body vessel lumen, such as in a vein. Implantable prosthetic stents or valves for veins often have the same compressibility or expandability in any radial direction. Similarly, implantable device configurations can be unresponsive to dynamic changes of the vessel cross-section, and can locally distort the shape of the body vessel.
There exists a need in the art for an implantable prosthetic device frame that is capable of better conforming to the shape of the vessel lumen, and being more responsive to dynamic changes in body vessel lumen shape. There is a further need for an intraluminal prosthetic device comprising an expandable frame or valve that can be deployed in vessels to replace or augment incompetent native valves, such that the frame or valve provides improved conformation to the shape of vein lumens and dynamic changes thereof. Such a device can closely simulate the normal vessel shape and responsiveness, as well as normal valve function, while being capable of permanent implantation with excellent biocompatibility.